faça o que eu digo, não faça o que eu faço

You use it as a disclaimer. Place it at the end of a piece of advice. It works best when the other person catches you doing the opposite. It turns a moment of hypocrisy into a moment of shared humor. You don't need to conjugate it differently; the standard form works for almost everyone.

Use it when you are caught in the act. Maybe you are telling a friend to save money while buying shoes. Or telling your kids to eat vegetables while you eat chocolate. It is perfect for mentors, parents, or friends who have "been there, done that."

Avoid using this in high-stakes professional environments. If you are a doctor telling a patient to quit smoking while holding a cigar, it might not go over well. Do not use it if you want to sound like a perfect role model. It admits fault, so don't use it if you need to maintain an image of absolute authority.

Portuguese speakers value authenticity but also love a good joke about human nature. This phrase likely has religious roots, referring to leaders who didn't practice their own sermons. Today, it is a staple of family life. Every Brazilian child has heard their parents say this at least once. It reflects a culture that understands humans are flawed and contradictory.

Sometimes people just say the first half: Faça o que eu digo. The rest is implied by the context. In very informal settings, you might hear people joke about ferreiro, espeto de pau, which is a related idiom about people not using their own skills at home. However, the full version remains the most recognizable and impactful way to call yourself out.